1. Technical Field
The disclosure relates to a clutch device in which frictional sliding between clutch plates is lubricated by lubricating oil.
2. Description of Related Art
A clutch device in which frictional sliding between clutch plates is lubricated by lubricating oil has been used as, for example, a driving force transmission device which transmits a driving force of a vehicle (see, for example, Japanese Patent Application Publication No. 2015-129574 (JP 2015-129574 A)).
The driving force transmission device described in JP 2015-129574 A includes an outer rotary member and an inner rotary member which are able to coaxially rotatable relative to each other; an electromagnetic clutch mechanism including pilot outer clutch plates and pilot inner clutch plates which are formed of a magnetic material such as iron; a cam mechanism which is activated by a torque transmitted by the electromagnetic clutch mechanism; and a main clutch including main outer clutch plates and main inner clutch plates, the main clutch being configured to connect the outer rotary member and the inner rotary member so as to allow torque transmission, in response to an axial pressing force provided by the earn mechanism.
The electromagnetic clutch mechanism includes an electromagnetic coil which generates a magnetic force when a current is applied to the electromagnetic coil; a yoke which holds the electromagnetic coil; and an armature which is drawn toward the yoke by the magnetic force of the electromagnetic coil. The pilot outer clutch plates and the pilot inner clutch plates are disposed between the yoke and the armature. When a current is applied to the electromagnetic coil, a torque of the outer rotary member is transmitted to the cam mechanism via the pilot outer clutch plates and the pilot inner clutch plates, and the cam mechanism is activated to press the main clutch.
Lubricating oil is sealed between the outer rotary member and the inner rotary member, and frictional sliding between the pilot outer and inner clutch plates and frictional sliding between the main outer and inner clutch plates are lubricated by the lubricating oil.
An inner peripheral spline part having a plurality of axially extending spline projections is formed on an inner peripheral surface of the outer rotary member. The pilot outer clutch plates and the main outer clutch plates engage with the inner peripheral spline part such that the pilot outer clutch plates and the main outer clutch plates are movable in an axial direction and are unable to rotate relative to the outer rotary member. A toothless part where no spline projection is formed is provided at a part of the inner peripheral spline part in the circumferential direction.
When a current is not applied to the electromagnetic coil, the lubricating oil is present between the pilot outer and inner clutch plates and between the main outer and inner clutch plates. When the current is applied to the electromagnetic coil, the lubricating oil present between the clutch plates flows in the axial direction, mainly via the toothless part and is discharged from an area between the clutch plates.